Process for producing a coil for a magnetic recording head

ABSTRACT

A process for producing a coil for a magnetic recording head and the coil obtained by this process. An insulating film which covers a support is etched in order to give it the shape of a first spiral. The support is then etched by using the insulating film as a mask, forming a groove in the form of a second spiral, which is complementary to the first spiral. A thin metal layer is then deposited on the insulating film used as the mask and simultaneously on the bottom of the etched groove, producing two conductors in the form of complementary spirals which are located in two different planes.

BACKGROUND OF THE INVENTION

The present invention relates to a process for producing a coil for amagnetic recording head and to a coil obtained by this process. It isused in the field of magnetic recording, disk memories, tape unreelingdevices, videoscopes, etc.

A magnetic recording head comprises an open magnetic circuit having anair gap and a coil surrounding a leg of the magnetic circuit. Onwriting, the passage of a current through the coil produces a leakagefield at the air gap permitting the writing of information in arecording layer in the vicinity thereof. On reading, a magnetic fluxvariation from the recording layer induces, at the terminals of thecoil, a potential difference constituting a reading signal.

A magnetic recording head coil generally comprises one or moreconductive spirals arranged in different planes. In order to producesuch a coil, a first conductive spiral is formed by deposition and thenetching of a metal layer, followed by the deposition of an insulatinglayer on the assembly. This process is repeated for forming a secondspiral on the insulating layer. The etching operations take placethrough masks and the two masks used are arranged in such a way that thetwo spirals are displaced from one another.

Such a procedure is more particularly described in the article by Y.NORO entitled "Fabrication of a multitrack thin-film head" published inthe Journal of Applied Physics, Vol. 53, 3, March 1982, pp. 2611-2613.

Although such processes are satisfactory in certain respects, they aredifficult to perform, particularly due to the double masking necessaryfor defining the coil. Thus, it is necessary to position the second maskwith considerable accuracy with respect to the first, or more preciselywith respect to the first spiral obtained.

SUMMARY OF THE INVENTION

The object of the present invention is to obviate this disadvantage byproposing a process only involving a single masking, but which stillmakes it possible to obtain two windings or coils.

According to the invention, this objective is achieved by a processfirstly comprising a conventional phase in the technology of depositingthin films, followed by a second original phase essentially consistingof depositing a conductive coating at the bottom of a spiral groove andsimultaneously on the material between two arms of the spiral. Thus, twoconductive spirals are simultaneously obtained in two different planes,the only masking involved being that making it possible to obtain thegroove. Thus, there is a self-alignment of the two conductive tapes.Moreover, the two spirals obtained are strictly complementary in that,viewed perpendicularly to their plane, the two spirals cover thecomplete plane. In the prior art, there is an overlap of the twospirals, which leads to breakdown risks.

More specifically, the present invention relates to a process forproducing a coil for a magnetic recording head in which an insulatingsupport is covered by a thin insulating film, the insulating film isetched by photolithography in order to give it the shape of a firstspiral with, at the centre, a wider area defining a future inner contactelement and, on the periphery, an area defining a future outer contactelement, the support is etched by using the insulating film as a mask,which leads to a groove in the form of a second spiral, which iscomplementary to the first, wherein a thin metal layer is deposited onthe assembly, i.e. on the insulating film used as the mask andsimultaneously at the bottom of the etched groove, which gives rise totwo conductors in the form of complementary spirals and located in twodifferent planes, said spirals terminating by an inner contact elementand an outer contact element, the thin metal layer has a small thicknesscompared with the depth of the groove, a photosensitive resin isdeposited on the assembly, followed by the removal of the resin outsidethe area of the spiral, and by etching, the superfluous metal layerdeposited on the insulating film outside these spirals is removed, theresin is removed and an electrical connection is made between the innercontact element of a spiral and the outer contact element of the otherspiral.

The invention also relates to a coil obtained by this process. On aninsulating support, the coil comprises two spiral conductors arranged intwo different planes, namely a lower plane and an upper plane. The twospirals are rigorously complementary to one another, the coil arrangedin the lower plane being positioned at the bottom of a groove etched inthe support.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail hereinafter relative tonon-limitative embodiments and the attached drawings, wherein show:

FIGS. 1, 2, 3, 4, 5, 6 and 7, in section, the main stages of the processaccording to the invention.

FIG. 8 the coil shown perpendicularly to its plane.

FIG. 9, in section, a magnetic recording head using the coil accordingto the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a support 2 formed from an electrically insulatingmaterial, such as e.g. glass, silica or an organic layer. This supportis covered with a thin film 4 with a thickness equal to or less than 1micron of an electrically insulating material and which can e.g. be anorganic layer of silica or silicon nitride. This film 4 must beselectively etchable with respect to support 2, in accordance with knownphotolithographic methods.

FIG. 2 illustrates the result of the etching of film 4. The materialleft behind delineates a spiral 3 with widened areas in the centre andon the periphery, as can best be seen in FIG. 8.

FIG. 3 illustrates the etching of a groove 5 obtained by using film 4 asa mask.

FIG. 4 shows an overetching of support 2 which, as it does not touchfilm 4, ensures that the latter overhangs each vertical wall of thegroove made in support 2.

FIG. 5 shows the deposition of an electrically conductive layer 6, whichcan be of copper or any other good electrically conductive material.This deposit preferably takes place under vacuum. It can be seen thatthe copper layer is deposited at the bottom of groove 5 and what is leftof film 4, without covering the vertical sides of the groove. Thesedeposits consequently define two complementary spirals without anyshort-circuit between them. These two spirals are in two differentplanes, the upper plane of film 4 and the bottom of the groove etched insupport 2.

FIG. 6 shows a photosensitive resin reservation 48 which, by etching,makes it possible to eliminate the superfluous portions of the depositof layer 6 on the plane of film 4.

FIG. 7 illustrates the final result.

FIG. 8 illustrates the shape of the coil, viewed perpendicularly to itsplane. The portion etched in support 2 is represented by the spiralstarting from the wider area 10 and finishing in the wider area 13. Thespiral obtained on the upper plane of film 4 starts in area 17 and endsin area 15. In order to form a double spiral with continuity of thewinding in the same direction, it is merely necessary to connect area 13to area 17 by known methods. The input of the coil will then be thecontact element 10 and its output will be the contact element 15, whichcan be more easily connected to a contact element 19.

FIG. 8 shows that the arms of the two spirals are strictly complementarywithout loss of space, which is obtained whilst still guaranteeing anexcellent insulation between each conductor. For example, if it is foundthat there is an irregularity 12 in the formation of the groove, thisirregularity will in no way modify the complementary nature of the twoconductive spirals, one of which is wider than the other, but in no casecan they encroach on one another. A precise etching can be obtained bychoosing insulating materials which can be easily etched, whilst themetal of layer 6 can only be finally etched with difficulty. Accordingto the invention, the metal is only etched in order to pass round thecontact elements 17, 19 or 15, which does not require high accuracy.

For all these reasons, a hard material will be used for film 4, such assilica or silicon nitride. Moreover, to obviate risks ofshort-circuiting between the two spirals, the thickness of the metaldeposit 6 will be limited to approximately 1/3 of the depth of thegroove. For example, the latter will be given a depth between 1.5 and 4μm, whilst the metal layer has a thickness between 0.5 and 1 μm.

FIG. 9 shows, in section, a magnetic head using the coil according tothe invention. Support 2 is deposited on a solid or thin film-typemagnetic material 20, which forms the first pole piece of the head. Asecond pole piece 22, which is also formed from solid or thin film-typemagnetic material is electrically insulated from the coil conductors byan electrically insulating coating 26. At the front of the head, an airgap 24 separates the pieces 20 and 22, whilst at the rear the two polepieces are joined, so as to close the magnetic circuit around the coil.In order to obtain a good magnetic efficiency of the head, it isimportant that the distance separating the air gap from the rear closingarea of the two pole pieces is as short as possible. To the extent thatit leads to adjacent conductors, the double spiral makes it possible toreduce said distance to a minimum, for a given conductor size. It wouldnaturally be possible to stack insulated double spirals a number oftimes.

What is claimed is:
 1. A process for producing a coil for a magneticrecording head, consisting of the steps of:covering an insulatingsupport with a thin insulating film, said film being selected from thegroup consisting of silica and silicon nitride; and etching theinsulating film by photolithography in order to give said film the shapeof a first spiral having a center and periphery, which said first spiralterminates at the center as a wider area defining a future inner contactarea, and terminates on the periphery as an area defining a future outercontact element; and etching the support by using the spiral-shapedinsulating film as a mask to form a groove in the shape of a secondspiral, which said second spiral is interleaved and couplementary to thefirst spiral, said groove having a groove bottom and a depth; anddepositing a thin metal layer simultaneously on the insulating film usedas the mask and on the bottom of the etched groove, which gives rise toa first conductor on the insulating film and a second conductor on thegroove bottom, which said first and second conductors are in the form ofcomplementary spirals to each other, and are located in two differenthorizontal planes, each of said spirals terminating by an inner contactelement and an outer contact element, the thin metal layer having athickness of approximately 1/3 of the depth of the groove; anddepositing a photosensitive resin completely over at least said spirals;and removing the resin outside said spirals; and removing, by etching,portions of the metal layer deposited on the insulating film outsidesaid spirals; and removing the remaining resin; and making an electricalconnection between the inner contact element of the first or secondspiral and the outer contact element of the other first or secondspiral.
 2. A process according to claim 1, wherein overetching of thesupport takes place always using the insulating film as the mask, whichhas the effect of making each insulating film overhang each verticalwall defining the groove.
 3. A process according to claim 1, wherein thegroove is given a depth between 1.5 and 4 μm.
 4. A process according toclaim 3, wherein the metal film is given a thickness between 0.5 and 1μm.